More than 80 years after Bartolomeo Vanzetti (left) and Nicola Sacco were executed in Massachusetts, historians question the validity of their murder trial, which critics say was conducted under a cloud of anti-immigrant sentiment. Courtesy photo.

Massachusetts filmmaker David Rothauser stars in the documentary "The Diary of Sacco and Vanzetti," which he also wrote and directed. The film will be shown April 13 in Londonderry. Courtesy photo.

More than 30 years ago, the Brookline, Mass., writer and director first gave birth to his film “The Diary of Sacco and Vanzetti” as a full-length screenplay including more than 50 characters. But over three decades in development, it narrowed into a 57-minute documentary with one central figure.

Seven years after its release, the movie is still showing before audiences across New England – it’s set to be shown later this month at the American Kenpo Academy in Londonderry. And that’s just how Rothauser pictured it from the start.

The film, released in 2004, uses letters, speeches and other authentic documents to tell the story of Nicola Sacco and Bartolomeo Vanzetti, Italian immigrants who were executed in Boston in 1927 after they were convicted of killing two people during a robbery in nearby Braintree, Mass., setting off a political firestorm.

The original screenplay “was very different from the film we ended up making. … But I always wanted it to be about their story,” said Rothauser, 55, who also stars in the film, taking the role of Vanzetti.

“I wanted to point out the injustice of it. I think we did a pretty good job sticking to that.”

The controversial trial, set against an anti-immigrant backdrop, was full of questionable evidence and wavering witnesses that first captured Rothauser’s attention when he was a young film student in the 1970s.

Fresh off of acting pursuits in Paris and New York City, Rothauser, who had started classes at Boston University, auditioned for the role of Vanzetti in a local play about the trial. To better prepare for the part, he started researching the case extensively, reading books and news accounts and conducting interviews that eventually formed the basis for his film.

“I interviewed a lot of people who knew Sacco and Vanzetti,” Rothauser said. “Sacco’s English teacher, I interviewed her in her hospital room” before she died.

“It was intense,” he said of his research.

After the play concluded its run, Rothauser’s script came together quickly – he completed it within a few months. But the financing didn’t come as easily.

Approaching local producers, Rothauser struggled over the ensuing years to raise the money necessary to put his vision to film. So, he moved on to other projects.

In 1984, he developed a documentary about German playwright Bertolt Brecht, which earned him honors from the American Film Festival in New York, and he took on full-time jobs teaching film at Fitchburg State College and Newbury College in Massachusetts.

But he never let go of the Sacco and Vanzetti project, and in 1996, he formed a production company, Memory Productions, to raise money for the movie.

“I had a lot of faith in David and his specific vision for the film,” said David Mauriello, a playwright and longtime friend of Rothauser’s, who helped finance the project, serving as an executive director.

“I just thought it was a very worthwhile project, and I knew he would do it well. It’s a phenomenal thing to watch.”

After six more years of fundraising, Rothauser finally set out in 2002 to film a pared-down version of his screenplay to match his $60,000 budget.

Film crews crossed the Boston area, shooting scenes at historic sites such as the Dedham Courthouse where the trial took place.

“It’s in the original condition,” Rothauser said.

And they recruited former Massachusetts Gov. Michael Dukakis to re-create the 1977 proclamation he read absolving Sacco and Vanzetti of the crimes.

“The anti-immigrant stuff then was just as rough then, if not more, than it is today,” Dukakis said. “It’s a history lesson that people ought to know.”

Once filming wrapped in 2004, producers took the documentary on the road, showing it across New England. It aired in 2004 and 2005 on WGBH-TV, and played locally in Bedford, among other locations, earning fans along the way.

“I thought it was fantastic, and being Italian, of course, it was a lot of history for (those of us) in the area,” said Viola Leonne, program manager for the Italian-American Heritage Society, which is sponsoring the film in Londonderry this month.

“It’s something that’s still relevant today,” said Leonne, who first saw the film in Bedford several years ago. “We’re a little more lenient now about ethnic groups than we were in the past. However, there’s a certain amount of prejudice still on the horizon.”

The film’s producers may still work to expand it to the full-length feature that was originally planned, Mauriello said.

But as it stands, the movie is still helping to promote better cultural and historical awareness, Rothauser said.

“If I had had a multimillion-dollar budget, I would have made a blockbuster,” he said. “But I think we ended up with what we needed. … The miscarriage of justice, you could say, is a universal message, the prejudice in the courtroom against foreigners.

“But in the end, it’s a story about these two men. … I’m glad we got a chance to tell it.”